Receiver apparatus having filters implemented using frequency translation techniques

ABSTRACT

A method and apparatus is disclosed to effectively frequency translate a filter characterized as a low quality factor (Q) filter corresponding to a baseband frequency of approximately zero Hertz or to an intermediate frequency (IF) to a filter characterized as a high Q filter at frequencies greater than the baseband frequency or the IF. A downconversion mixer is used to frequency translate a communication signal to the baseband frequency or the IF using a first local oscillator signal to provide a downconverted communication signal. A filter characterized as the low Q filter corresponding to the baseband frequency or the IF filters the downconverted communication signal to provide a filtered communication signal. An upconversion mixer is used to frequency translate a communication signal using a second local oscillator signal, the second local oscillator signal being substantially similar in frequency of the first local oscillator signal. The frequency translation by the upconversion mixer, in effect, translates the filter characterization from the low Q filter to the high Q filter at frequencies greater than the baseband frequency or the IF.

FIELD OF THE INVENTION

This application relates generally to filters and, more specifically, tohigh quality factor (Q) filters.

BACKGROUND

There exist two commonly implemented front-end architectures in radiofrequency (RF) receiver design; namely, the homodyne architecture andthe heterodyne architecture. The homodyne architecture down-converts adesired channel directly from RF to substantially zero Hertz, referredto as baseband, or a low intermediate frequency (IF). The heterodynearchitecture down-converts a desired channel to one or more intermediatefrequencies (IF) before down-conversion to baseband. In general, each ofthese front-end architectures typically employ an antenna to receive anRF signal, a band-pass filter to suppress out-of-band interferers in thereceived RF signal, a low noise amplifier (LNA) to provide gain to thefiltered RF signal, and one or more down-conversion stages.

Each component in a receiver front-end contributes noise to the overallsystem. The noise of a component can be characterized by its noisefigure (NF), which is given by the ratio of the SNR at the input of thecomponent to the SNR at the output of the component:

$\begin{matrix}{{NF}_{COMPONENT} = {\frac{{SNR}_{IN}}{{SNR}_{OUT}}.}} & (1)\end{matrix}$The noise of the overall receiver front-end increases from input tooutput as noise from successive components compound. In general, theoverall noise figure of the receiver front-end is proportional to thesum of each component's noise figure divided by the cascaded gain ofpreceding components and is given by:

$\begin{matrix}{{{NF}_{TOTAL} = {{NF}_{1} + \frac{{NF}_{2 - 1} - 1}{A_{1}} + \frac{{NF}_{2 - 1} - 1}{\prod\limits_{i = 1}^{2}A_{i}} + \ldots + \frac{{NF}_{n - 1} - 1}{\prod\limits_{i = 1}^{n}A_{i}}}},} & (2)\end{matrix}$where NF_(n) and A_(n) represent the noise figure and gain of the n^(th)component in the receiver front-end, respectively. The above equationreveals that the noise figure (NF₁) and gain (A₁) of the first gaincomponent can have a dominant effect on the overall noise figure of thereceiver front-end, since the noise contributed by each successivecomponent is diminished by the cascaded gain of the components thatprecede it.

To provide adequate sensitivity, therefore, it is important to keep thenoise figure (NF₁) low and the gain (A₁) high of the first gaincomponent in the receiver front-end. The sensitivity of the receiverfront-end determines the minimum signal level that can be detected andis limited by the overall noise figure of the receiver front-end. Thus,in typical receiver designs the first gain component in the front-end isan LNA, which can provide high gain, while contributing low noise to theoverall RF receiver.

LNAs provide relatively linear gain for small signal inputs. However,for sufficiently large input signals, LNAs can exhibit non-linearbehavior in the form of gain compression; that is, for sufficientlylarge input signals, the gain of the LNA approaches zero. LNA gaincompression is a common issue confronted in RF receiver design, sincelarge out-of-band interferers referred to as blockers can accompany acomparatively weak desired signal in a received RF signal. For example,in the Global System for Mobile Communications (GSM) standard, a desiredsignal 3 dB above sensitivity (−102 dBm) can be accompanied by a 0 dBmblocker as close as 80 MHz away. If these large out-of-band interferersare not attenuated prior to reaching the LNA, they can reduce theaverage gain of the LNA. As noted above, a reduction in the gainprovided by the LNA leads to an increase in the noise figure of thereceiver front-end and a corresponding degradation in sensitivity.

Therefore, a band-pass filter is conventionally employed in the receiverfront-end, before the LNA, to attenuate large out-of-band interferers.These filters are typically mechanically-resonant devices, such assurface acoustic wave (SAW) filters, that provide a high quality factor(Q) required by many of today's communication standards (e.g., GSM). TheQ-factor of a tuned circuit, such as a band-pass filter, is the ratio ofits resonant frequency (or center frequency) to its 3 dB frequencybandwidth. SAW filters are generally not amenable to monolithicintegration on a semiconductor substrate with the RF receiver. However,SAW filters remain conventional in RF receiver design because of thelimited Q-factor of silicon-based inductors.

Although SAW filters can provide excellent attenuation of largeout-of-band interferers and accurate pass-band location, they haveseveral associated disadvantages. First, these filters have anapproximate insertion loss of 1-2 dB in their pass-band. This directlyadds to the noise figure and degrades sensitivity of the RF receiver.Second, these filters invariably add cost and circuit board area,especially in multi-band applications where several of these filters canbe required.

Therefore, there exists a need for an apparatus that provides adequateattenuation of large out-of-band interferers on a semiconductorsubstrate, while accommodating wideband applications

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 illustrates a block diagram of a communications environmentaccording to an exemplary embodiment of the present invention.

FIG. 2 illustrates a block diagram of a communications transceiver usedin the communications environment according to an exemplary embodimentof the present invention.

FIG. 3 illustrates a first block diagram of a communications receiverused in the communications transceiver according to a first exemplaryembodiment of the present invention.

FIG. 4 graphically illustrates a frequency translation of a filtermodule used in the communications receiver according to an exemplaryembodiment of the present invention.

FIG. 5 illustrates a second block diagram of a communications receiverused in the communications transceiver according to a second exemplaryembodiment of the present invention.

FIG. 6A illustrates a third block diagram of a communications receiverused in the communications transceiver according to a third exemplaryembodiment of the present invention.

FIG. 6B illustrates a fourth block diagram of a communications receiverused in the communications transceiver according to a fourth exemplaryembodiment of the present invention.

FIG. 7 illustrates a fifth block diagram of a communications receiverused in the communications transceiver according to a fifth exemplaryembodiment of the present invention.

FIG. 8 illustrates a block diagram of an amplifier module used in thecommunications receiver according to an exemplary embodiment of thepresent invention.

FIG. 9 illustrates a block diagram of a filter module used in thecommunications receiver according to an exemplary embodiment of thepresent invention.

FIG. 10 is a flowchart of exemplary operational steps of thecommunications receiver used in the communications transceiver accordingto an exemplary embodiment of the present invention.

The present invention will be described with reference to theaccompanying drawings. The drawing in which an element first appears istypically indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION OF THE INVENTION

The following Detailed Description refers to accompanying drawings toillustrate exemplary embodiments consistent with the invention.References in the Detailed Description to “one exemplary embodiment,”“an exemplary embodiment,” “an example exemplary embodiment,” etc.,indicate that the exemplary embodiment described may include aparticular feature, structure, or characteristic, but every exemplaryembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same exemplary embodiment. Further, when a particularfeature, structure, or characteristic is described in connection with anexemplary embodiment, it is within the knowledge of those skilled in therelevant art(s) to effect such feature, structure, or characteristic inconnection with other exemplary embodiments whether or not explicitlydescribed.

The exemplary embodiments described herein are provided for illustrativepurposes, and are not limiting. Other exemplary embodiments arepossible, and modifications may be made to the exemplary embodimentswithin the spirit and scope of the invention. Therefore, the DetailedDescription is not meant to limit the invention. Rather, the scope ofthe invention is defined only in accordance with the following claimsand their equivalents.

The following Detailed Description of the exemplary embodiments will sofully reveal the general nature of the invention that others can, byapplying knowledge of those skilled in relevant art(s), readily modifyand/or adapt for various applications such exemplary embodiments,without undue experimentation, without departing from the spirit andscope of the present invention. Therefore, such adaptations andmodifications are intended to be within the meaning and plurality ofequivalents of the exemplary embodiments based upon the teaching andguidance presented herein. It is to be understood that the phraseologyor terminology herein is for the purpose of description and not oflimitation, such that the terminology or phraseology of the presentspecification is to be interpreted by those skilled in relevant art(s)in light of the teachings herein.

Communications Environment

FIG. 1 illustrates a block diagram of a communications environmentaccording to an exemplary embodiment of the present invention. Thecommunications environment 100 includes a first communicationstransceiver 102 to transmit one or more first information signals,denoted as a first information signal 150, as received from one or morefirst transceiver user devices to a second communications transceiver106 via a communications channel 104. The one or more first transceiveruser devices may include, but are not limited to, personal computers,data terminal equipment, telephony devices, broadband media players,personal digital assistants, software applications, or any other devicecapable of transmitting or receiving data. The first communicationstransceiver 102 provides a first transmitted communications signal 152based upon the first information signal 150.

The first transmitted communications signal 152 passes through thecommunications channel 104 to provide a first received communicationssignal 154. The communications channel 104 may include, but is notlimited to, a microwave radio link, a satellite channel, a fiber opticcable, a hybrid fiber optic cable system, or a copper cable to providesome examples. The communications channel 104 contains a propagationmedium that the first transmitted communications signal 152 passesthrough before reception by the communications receiver 106. Thepropagation medium of the communications channel introduces interferenceand/or distortion into the first transmitted communications signal 152causing a first received communications signal 154 to differ from thefirst transmitted communications signal 152. For example, thecommunications channel 104 may introduce interference and/or distortionresulting from undesirable signals, referred to as interferers, into thefirst transmitted communications signal 152. This interference may beinclusive within a bandwidth occupied by the first transmittedcommunications signal 152, referred to as in band interference, and/orexclusive within the bandwidth occupied by the first transmittedcommunications signal 152, referred to as out-of-band interference.

The second communications transceiver 106 receives the first receivedcommunications signal 154 as it passes through the communicationschannel 104 to provide one or more first recovered information signals,denoted as a first recovered information signal 156, for one or moresecond transceiver user devices. The one or more second transceiver userdevices may include, but are not limited to, personal computers, dataterminal equipment, telephony devices, broadband media players, personaldigital assistants, software applications, or any other device capableof transmitting or receiving data.

The second communications transceiver 106 transmits one or more secondinformation signals, denoted as a second information signal 158, asreceived from the one or more second transceiver user devices to thefirst communications transceiver 102 via the communications channel 104.The second communications transceiver 106 provides a second transmittedcommunications signal 160 based upon the second information signal 158.

The second transmitted communications signal 160 passes through thecommunications channel 104 to provide a second received communicationssignal 162. The first communications transceiver 102 receives the secondreceived communications signal 162 as it passes through thecommunications channel 104 to provide one or more second recoveredinformation signals, denoted as a second recovered information signal164, for the one or more first transceiver user devices.

Communications Transceiver

FIG. 2 illustrates a block diagram of a communications transceiver usedin the communications environment according to an exemplary embodimentof the present invention. A communications transceiver 200 provides apresented communications signal 252 based upon an information signal 250and/or a recovered information signal 254 based upon an observedcommunications signal 256. The communications transceiver 200 mayrepresent an exemplary embodiment of the first communicationstransceiver 102 and/or the second communications transceiver 106 asdescribed above. Likewise, the presented communications signal 252 mayrepresent an exemplary embodiment of the first transmittedcommunications signal 152 and/or the second transmitted communicationssignal 156 as described above. Similarly, the observed communicationssignal 256 may represent an exemplary embodiment of the first receivedcommunications signal 154 and/or the second received communicationssignal 162 as described above.

The communications transceiver 200 includes a communications transmitter202, a communications receiver 204, and a selection module 206. Thecommunications transmitter 202 provides a transmitted communicationssignal 258 based upon the information signal 250. The functionality ofthe communications transmitter 202 may include filtering of, encodingof, modulating of, and/or error correction of the information signal250. However these examples are not limiting, those skilled in therelevant art(s) may implement the communications transmitter 202 toinclude any other suitable function(s) without departing from the spiritand scope of the present invention.

The communications receiver 204 provides recovered information signal254 based upon a received communications signal 260. The functionalityof the communications receiver 204 may include filtering of, decodingof, demodulating of and/or error correction of the receivedcommunications signal 260. However these examples are not limiting,those skilled in the relevant art(s) may implement the communicationsreceiver 204 to include any other suitable function(s) without departingfrom the spirit and scope of the present invention.

The selection module 206 provides the transmitted communications signal258 as the presented communications signal 252 to the communicationschannel 104 via one or more antennas, one or more copper cables, one ormore fiber optic cables, and/or any other suitable means that will beapparent to those skilled in the relevant art(s). Likewise, theselection module 206 provides the observed communications signal 256 asthe received communications signal 260 from the communications channel104 via the one or more antennas, the one or more copper cables, the oneor more fiber optic cables, and/or the any other suitable means thatwill be apparent to those skilled in the relevant art(s). The selectionmodule 206 may present the presented communications signal 252 using asimilar device that is used to observe the observed communicationssignal 256 or one or more dissimilar devices. For example, the selectionmodule 206 may present the presented communications signal 252 to asingle antenna and observe the observed communications signal 256 fromthe single antenna. As another example, the selection module 206 maypreserve the presented communications signal 252 to a single antenna andobserve the observed communications signal 256 from one or more coppercables.

The selection module 206 may be configured to operate in a half-duplexmode of operation or a full-duplex mode of operation. In the half-duplexmode of operation, the selection module 206 may operate in a transmitmode of operation to present the presented communications signal 252 tothe communications channel 104. Alternatively, the selection module 206may operate in a receive mode of operation to observe the observedcommunications signal 256 from the communications channel 104. In anexemplary embodiment, the selection module 206 includes a switch toselect from among the transmit mode of operation and the receive mode ofoperation. Alternatively, the selection module 206 may be configured tooperate in the full-duplex mode of operation. In the full-duplex mode ofoperation, the selection module 206 may simultaneously operate in thetransmit mode of operation and the receive mode of operation.

One or more of the communications transmitter 202, the communicationsreceiver 204, and the selection module 206 may be implemented on acommon chip or die. Alternatively, the one or more of the communicationstransmitter 202, the communications receiver 204, and the selectionmodule 206 may be each implemented on a single chip or die. The commonchips or dies and/or the single chips or dies may be connected togetherusing bond wires and/or any other suitable means that will be apparentto those skilled in the relevant art(s) to form a part of thecommunications transceiver 200.

FIRST EMBODIMENT OF A COMMUNICATIONS RECEIVER

FIG. 3 illustrates a first block diagram of a communications receiverused in the communications transceiver according to a first exemplaryembodiment of the present invention. A communications receiver 300provides a digital recovered information signal 350 based upon areceived communications signal 260. The communications receiver 300 mayrepresent an exemplary embodiment of communications receiver 204. Thecommunications receiver 300 includes a combination module 302, anamplifier module 304, a downconversion mixer 306, a first filter module308, an upconversion mixer 310, a second filter module 312, and ananalog to digital converter (ADC) 314.

The combination module 302 combines the received communications signal260 and an upconverted replica noise signal 364, to be discussed infurther detail below, to provide a noise reduced communications signal352. The received communications signal 260 includes a desiredcommunications signal and out of band interference, the out of bandinterference occupying a spectrum of frequencies that is exclusive froma spectrum of frequencies occupied by the desired communications signal.In other words, the out of band interference may be located outside,that is less than and/or greater than, a spectrum of frequenciesoccupied by the desired communications signal, commonly referred to as abandwidth of the desired communications signal. The combination module302, in effect, substantially reduces the out of band interferenceembedded within the received communications signal 260 by subtractingthe upconverted replica noise signal 364 from the receivedcommunications signal 260 to provide the noise reduced communicationssignal 352.

The amplifier module 304 amplifies the noise reduced communicationssignal 352 to provide an amplified communications signal 354. Morespecifically, the amplifier module 304 amplifies the noise reducedcommunications signal 352 by a gain G₁ to provide the amplifiedcommunications signal 354. In an exemplary embodiment, the amplifiermodule 304 is implemented using a low noise amplifier (LNA).

The downconversion mixer 306 downconverts the amplified communicationssignal 354 using a first local oscillator signal 356 to provide arecovered communications signal 358. The recovered communications signal358 includes the desired communications signal and the out of bandinterference, each of which has been frequency translated by the firstlocal oscillator signal 356. The downconversion mixer 306 maydownconvert or frequency translate the amplified communications signal354 directly to approximately zero Hertz, referred to as DC or baseband,or to an intermediate frequency (IF) that is greater than DC to providethe recovered communications signal 358.

The first filter module 308 filters the recovered communications signal358 to provide a replica noise signal 360, the replica noise signal 360being proportional to the out of band interference embedded withinrecovered communications signal 358. More specifically, the first filtermodule 308 may implement a high pass filtering topology to filter out orremove the desired communications signal embedded within the recoveredcommunications signal 358, leaving only the out of band interferenceembedded within the recovered communications signal 358 as the replicanoise signal 360. Alternatively, in addition to removing the desiredcommunications signal embedded within the recovered communicationssignal 358, the first filter module 308 may implement a bandpassfiltering topology to additionally filter out any higher ordered mixingproducts, such as any sum and/or difference products to provide someexamples, embedded within the recovered communications signal 358. Thesehigher ordered mixing products represent undesirable mixing productsresulting from the frequency translation of the amplified communicationssignal 354 by the downconversion mixer 306.

The upconversion mixer 310 upconverts the replica noise signal 360 usinga second local oscillator signal 362 to provide the upconverted replicanoise signal 364. The upconversion mixer 310 may upconvert or frequencytranslate the replica noise signal 360 to a frequency of the secondlocal oscillator signal 362. In an exemplary embodiment, the frequencyof the second local oscillator signal 362 is substantially similar to afrequency of the first local oscillator signal 356. In another exemplaryembodiment, the frequency of the second local oscillator signal 362 issubstantially similar to a frequency of the first local oscillatorsignal 356 but offset in phase from each other. The offset in phasebetween the first local oscillator signal 356 and the second localoscillator signal 362 ensures that the out of band interference embeddedwithin the received communications signal 260 and the upconvertedreplica noise signal 364 are substantially aligned in phase. Forexample, in this exemplary embodiment, the frequency of the first localoscillator signal 356 may be represented as:cos(ω_(LO)t),  (3)and the second local oscillator signal 362 may be represented as:cos(ω_(LO)t+φ),  (4)where φ represents a phase offset between the first local oscillatorsignal 356 and the second local oscillator signal 362. In an additionalexemplary embodiment, the phase offset φ may be substantially similar toa group delay of the first filter module 308. Alternatively, the phaseoffset φ may represent as programmable phase offset between 0 and 2π,such as

$\frac{n\;\pi}{2},$where n represents 1, 2, 3. or 4. to provide an example. However, theseexamples are not limiting, those skilled in the relevant art(s) may useany suitable phase offset φ to substantially align the out of bandinterference embedded within the received communications signal 260 andthe upconverted replica noise signal 364 in phase without departing fromthe spirit and scope of the present invention.

The second filter module 312 filters the recovered communications signal358 to provide a recovered information signal 366. The second filtermodule 312 may implement a low pass filtering topology to filter out orremove the out of band interference embedded within the recoveredcommunications signal 358 leaving only the desired communications signalembedded within the recovered communications signal 358 as the recoveredinformation signal 366.

The analog to digital converter (ADC) 314 converts the recoveredinformation signal 366 from an analog representation to a digitalrepresentation to provide the digital recovered information signal 350.The digital recovered information signal 350 may be provided to adigital signal processing device (not shown in FIG. 3) to furtherprocess the digital recovered information signal 350 to provide therecovered information signal 254. Alternatively, the ADC 314 maydirectly provide the provide the digital recovered information signal350 as the recovered information signal 254.

Filter Module Used in the Communications Receiver

FIG. 9 illustrates a block diagram of a filter module used in thecommunications receiver according to an exemplary embodiment of thepresent invention. In this exemplary embodiment, the first filter module308 may implement a bandpass filtering topology to filter out or removethe desired communications signal and any higher ordered mixingproducts, such as any sum and/or difference products to provide someexamples, embedded within the recovered communications signal 358.However, this example is not limiting, those skilled in the relevantart(s) may implement the first filter module 308 using any othersuitable filter topology, such as low pass, high pass, and band stop toprovide some examples, differentially in accordance with the teachingsherein without departing from the spirit and scope of the presentinvention.

The filter module 308 includes a high pass stage 902 and a low passstage 904. The high pass stage 902 removes the desired communicationssignal embedded within the recovered communications signal 358 using aseries capacitor C₁ coupled to a shunt resistor R₁. The low pass stage904 removes the higher ordered mixing products embedded within therecovered communications signal 358 using includes a series resistor R₂coupled to a shunt capacitor C₂.

Frequency Translation of the Filter Module

The frequency translation of the amplified communications signal 354 bythe downconversion mixer 306, the filtering of the recoveredcommunications signal 358 by the first filter module 308, and thesubsequent frequency translation of the replica noise signal 360 by theupconversion mixer 310, in effect, frequency translates a frequencyresponse, as indicated by determined by a transfer function, of thefirst filter module 308 from the baseband or the IF frequencies to thefrequency of the second local oscillator signal 362.

FIG. 4 graphically illustrates a frequency translation of a filtermodule used in the communications receiver according to an exemplaryembodiment of the present invention. The filter module 308 may becharacterized by its respective resonant frequency (or center frequency)and its 3 decibel (dB) frequency bandwidth. The quality factor (Q) thefirst filter module 308 is the ratio of its resonant frequency (orcenter frequency) to its 3 decibel (dB) frequency bandwidth. As shown inspectrum graph 402, at the baseband or the IF frequencies, the resonantfrequency and the 3 dB frequency bandwidth, denoted as a differencebetween of the first filter module 308 are both low, such in the orderof Megahertz (MHz) or Kilohertz (KHz) to provide some examples,resulting in a low Q filter at these frequencies. The Q factor of thefirst filter module 308 at the baseband or the IF frequencies may bedenoted as:

$\begin{matrix}{\frac{f_{RX}}{f_{H} - f_{L}},} & (5)\end{matrix}$where f_(RX) represents the resonant frequency of the first filtermodule 308 and f_(H)−f_(L) represents the 3 dB frequency bandwidth ofthe first filter module 308.

As shown in spectrum graph 404, the subsequent frequency translation ofthe replica noise signal 360 by the upconversion mixer 310, in effect,frequency translates the first filter module 308 from being a low Qfilter at the baseband or the IF frequencies to a high Q filter at thefrequency of the second local oscillator signal 362. The Q factor of thefirst filter module 308 at the frequency of the second local oscillatorsignal 362 may be denoted as:

$\begin{matrix}{\frac{f_{LO}}{f_{H} - f_{L}},} & (6)\end{matrix}$where f_(LO) represents the frequency of the second local oscillatorsignal 362 and f_(H)−f_(L) represents the 3 dB frequency bandwidth ofthe first filter module 308 at baseband. The resonant frequency of thefirst filter module 308 is translated from a low resonant frequency to ahigh resonant frequency, such as in the order Gigahertz (GHz) to providean example, resulting in a higher Q filter. The 3 dB frequency bandwidthof the first filter module 308 remains, however, unchanged at thefrequency of the second local oscillator signal 362. In other words, the3 dB frequency bandwidth of the first filter module 308 is maintained atbaseband at the frequency of the second local oscillator signal 362. Asa result, the effective ratio of its resonant frequency to its 3 decibelfrequency bandwidth, or the Q factor, effectively increases whencompared to the Q factor at the baseband or the IF frequencies.

Although the frequency translation of the frequency response of thefirst filter module 308 is described in terms of a bandpass filter inFIG. 4, those skilled in the relevant art(s) may similarly frequencytranslate any other filter topology, such as low pass, high pass, andband stop to provide some examples, in a substantially similar manneraccordance with the teachings herein without departing from the spiritand scope of the present invention.

SECOND EMBODIMENT OF THE COMMUNICATIONS RECEIVER

Quadrature modulating entails modulating an information signal, such asthe first information signal 150 and/or the second information signal158 to provide some examples, with two carrier waves that aresubstantially similar in frequency but exhibit a 90-degree phase offsetfrom one another. The information signal is substantially simultaneouslymodulated with a first carrier wave to provide an in-phase (I) signaland a second carrier to provide a quadrature phase (Q) signal. The Isignal and Q signal are then combined to provide a transmittedcommunication signal, such as the first transmitted communicationssignal 152 and/or the second transmitted communications signal 160 toprovide some examples.

FIG. 5 illustrates a second block diagram of a communications receiverused in the communications transceiver according to a second exemplaryembodiment of the present invention. A communications receiver 500provides an in-phase digital recovered information signal 350 a and aquadrature phase digital recovered information signal 350 b based uponthe received communications signal 260. The received communicationssignal 260 may be modulated and/or encoded using a quadrature scheme,such as phase-shift keying (PSK), or quadrature amplitude modulation(QAM) to provide some examples. The communications receiver 500 mayrepresent an exemplary embodiment of communications receiver 204. Thecommunications receiver 500 includes the first combination module 302,the amplifier module 304, the downconversion mixer 306, the first filtermodule 308, the upconversion mixer 310, the second filter module 312,the ADC 314, and a second combination module 502. The communicationsreceiver 500 operates in a substantially similar manner as thecommunications receiver 300. Therefore, only differences between thecommunications receiver 300 and the communications receiver 500 will befurther described in detail.

The downconversion mixer 306 includes an in-phase downconversion mixer306 a and a quadrature phase downconversion mixer 306 b. The in-phasedownconversion mixer 306 a downconverts the amplified communicationssignal 354 using an in-phase first local oscillator signal 356 a toprovide an in-phase recovered communications signal 358 a. The seconddownconversion mixer 306 b downconverts the amplified communicationssignal 354 using a quadrature phase first local oscillator signal 356 bto provide a quadrature phase recovered communications signal 358 b. Thein-phase downconversion mixer 306 a and the quadrature phasedownconversion mixer 306 b operate in a substantially similar manner asthe downconversion mixer 306 as described above. The in-phase firstlocal oscillator signal 356 a and the quadrature phase first localoscillator signal 356 b are substantially similar in frequency butoffset in phase by 90-degrees.

The first filter module 308 includes an in-phase first filter module 308a and a quadrature phase first filter module 308 b. The in-phase firstfilter module 308 a filters the in-phase recovered communications signal358 a to provide an in-phase replica noise signal 360 a, the in-phasereplica noise signal 360 a being proportional to the out of bandinterference embedded within the in-phase recovered communicationssignal 358 a. The quadrature phase first filter module 308 b filters thequadrature phase recovered communications signal 358 b to provide aquadrature phase replica noise signal 360 b, the quadrature phasereplica noise signal 360 b being proportional to the out of bandinterference embedded within the quadrature phase recoveredcommunications signal 358 b. The in-phase first filter module 308 a andthe quadrature phase first filter module 308 b operate in asubstantially similar manner as the first filter module 308 as describedabove.

The upconversion mixer 310 includes an in-phase upconversion mixer 310 aand a quadrature phase upconversion mixer 310 b. The in-phaseupconversion mixer 310 a upconverts the in-phase replica noise signal360 a using an in-phase second local oscillator signal 362 a to providean in-phase upconverted replica noise signal 550 a. The quadrature phaseupconversion mixer 310 b upconverts the quadrature phase replica noisesignal 360 b using a quadrature phase second local oscillator signal 362b to provide the quadrature phase upconverted replica noise signal 550b. The in-phase downconversion upconversion mixer 310 a and thequadrature phase upconversion mixer 310 b operate in a substantiallysimilar manner as the upconversion mixer 310 as described above. Thein-phase second local oscillator signal 362 a and the quadrature phasesecond local oscillator signal 362 b are substantially similar infrequency but offset in phase by 90-degrees.

The second combination module 502 combines the in-phase upconvertedreplica noise signal 550 a and the quadrature phase upconverted replicanoise signal 550 a to provide the upconverted replica noise signal 364.

The second filter module 312 includes an in-phase second filter module312 a and a quadrature phase second filter module 312 b. The in-phasesecond filter module 312 a filters the in-phase recovered communicationssignal 358 a to provide an in-phase recovered information signal 366 a.The quadrature phase second filter module 312 b filters the quadraturephase recovered communications signal 358 b to provide a quadraturephase recovered information signal 366 b. The in-phase second filtermodule 312 a and the quadrature phase second filter module 312 b operatein a substantially similar manner as the second filter module 312 asdescribed above.

The ADC 314 includes an in-phase ADC 314 a and a quadrature phase ADC314 b. The in-phase ADC 314 a converts the in-phase recoveredinformation signal 366 a from an analog representation to a digitalrepresentation to provide the in-phase digital recovered informationsignal 350 a. The quadrature phase ADC 314 b converts the quadraturephase recovered information signal 366 b from an analog representationto a digital representation to provide the quadrature phase digitalrecovered information signal 350 b. The in-phase ADC 314 a and thequadrature phase ADC 314 b operate in a substantially similar manner asthe ADC 314 as described above.

THIRD EMBODIMENT OF THE COMMUNICATIONS RECEIVER

FIG. 6A illustrates a third block diagram of a communications receiverused in the communications transceiver according to a third exemplaryembodiment of the present invention. A communications receiver 600provides a digital recovered information signal 350 based upon areceived communications signal 260. The communications receiver 600 mayrepresent an exemplary embodiment of communications receiver 204. Thecommunications receiver 600 includes the combination module 302, theamplifier module 304, the downconversion mixer 306, the first filtermodule 308, the upconversion mixer 310, the second filter module 312,the ADC 314, and a second amplifier module 602. The communicationsreceiver 600 operates in a substantially similar manner as thecommunications receiver 300. Therefore, only differences between thecommunications receiver 300 and the communications receiver 500 will befurther described in detail.

The second amplifier module 602 amplifies the recovered communicationssignal 358 to provide an amplified recovered communications signal 650.The first filter module 308 and the second filter module 312 may filterthe amplified recovered communications signal 650 to provide the replicanoise signal 360 and the recovered information signal 366, respectively.In an exemplary embodiment, the second amplifier module 602 isimplemented as a buffering amplifier having a gain of approximately one.In this exemplary embodiment, the second amplifier module 602substantially reduces reflections from the first filter module 308and/or the second filter module 312 from substantially degrading theperformance of the downconversion mixer 306.

FOURTH EMBODIMENT OF THE COMMUNICATIONS RECEIVER

It should be noted that the communications receiver 500 may also bemodified in a substantially similar manner. FIG. 6B illustrates a fourthblock diagram of a communications receiver used in the communicationstransceiver according to a fourth exemplary embodiment of the presentinvention.

A communications receiver 620 provides a digital recovered informationsignal 350 based upon a received communications signal 260. Thecommunications receiver 600 may represent an exemplary embodiment ofcommunications receiver 204. The communications receiver 600 includesthe combination module 302, the amplifier module 304, the downconversionmixer 306, the first filter module 308, the upconversion mixer 310, thesecond filter module 312, the ADC 314, and a second amplifier module602. The communications receiver 620 operates in a substantially similarmanner as the communications receiver 500. Therefore, only differencesbetween the communications receiver 500 and the communications receiver620 will be further described in detail.

An in-phase second amplifier module 602 a provides an in-phase amplifiedrecovered communications signal 650 a and a quadrature phase secondamplifier module 602 b to provide a quadrature phase amplified recoveredcommunications signal 650 b. The in-phase first filter module 308 a andthe in-phase second filter module 312 a may then filter the in-phaseamplified recovered communications signal 650 a to provide the in-phasereplica noise signal 360 a and the in-phase recovered information signal366 a, respectively. Likewise, the quadrature phase first filter module308 b and the quadrature phase second filter module 312 b may filter thequadrature phase amplified recovered communications signal 650 b toprovide the quadrature phase replica noise signal 360 b and thequadrature phase recovered information signal 366 b, respectively.

FIFTH EMBODIMENT OF THE COMMUNICATIONS RECEIVER

FIG. 7 illustrates a fifth block diagram of a communications receiverused in the communications transceiver according to a fifth exemplaryembodiment of the present invention. A communications receiver 700provides a digital recovered information signal 350 based upon areceived communications signal 260. The communications receiver 700 mayrepresent an exemplary embodiment of communications receiver 204. Thecommunications receiver 700 includes the combination module 302, theamplifier module 304, the downconversion mixer 306, the first filtermodule 308, the upconversion mixer 310, the second filter module 312,the ADC 314, and a second amplifier module 702. The communicationsreceiver 700 operates in a substantially similar manner as thecommunications receiver 300. Therefore, only differences between thecommunications receiver 300 and the communications receiver 500 will befurther described in detail.

The second amplifier module 702 amplifies the received communicationssignal 260 by a gain G₂ to provide an amplified received communicationssignal 752. The second amplifier module 702 amplifies the receivedcommunications signal 260 by the gain G₂ to provide an amplifiedreceived communications signal 752. The gain G₂ is selected such thatthe amplification of the out of band interference embedded within thereceived communications signal 260 does not cause the second amplifiermodule 702 to compress.

The out of band interference embedded within the received communicationssignal 260 may be substantially reduced by combining the amplifiedreceived communications signal 752 and the upconverted replica noisesignal 364. However, this combing introduces additional undesirableinterference and/or distortion resulting from the downconversion mixer306, the first filter module 308, and/or the upconversion mixer 310 intothe noise reduced communications signal 352. By dividing the overallgain of the communications receiver 700 into the gain G₁ and the gainG₂, the gain G₁ of the amplifier module 304 of the communicationsreceiver 700 may be reduced from the gain G₁ of the amplifier module 304used in the communications receiver 300, thereby reducing theamplification of the additional undesirable interference and/ordistortion.

It should be noted that the communications receiver 500 and thecommunications receiver 600 may be modified in a substantially similarmanner to include a second amplifier module 702.

FIG. 8 illustrates a block diagram of an amplifier module used in thecommunications receiver according to an exemplary embodiment of thepresent invention. An amplifier module 800 amplifies a firstcommunications signal 850 by a gain G₁ using a first amplifier module802 to provide an amplified first communications signal 852. The firstamplifier module 802 may represent an exemplary embodiment of the secondamplifier module 702. Likewise, the first communications signal 850 andthe amplified first communications signal 852 may represent exemplaryembodiments of the received communications signal 260 and the amplifiedreceived communications signal 752, respectively. The first amplifiermodule 802 includes an n-type metal oxide silicon (NMOS) transistor M₁and an inductor L₁ configured and arranged to operate as a common sourcetransistor amplifier.

The amplifier module 800 combines the first communications signal 850with a second communications signal 854 using a combination module 804to provide a noise-reduced communications signal 856. The combinationmodule 804 may represent an exemplary embodiment of the combinationmodule 302. Likewise, the second communications signal 854 and thenoise-reduced communications signal 856 may represent exemplaryembodiments of upconverted replica noise signal 364 and the noisereduced communications signal 352, respectively. The combination module804 is implemented as a simple circuit node.

The amplifier module 800 amplifies noise-reduced communications signal856 by a gain G₂ using a second amplifier module 806 to provide anoise-reduced communications signal 858. The second amplifier module 806may represent an exemplary embodiment of the amplifier module 304.Likewise, the noise-reduced communications signal 858 may represent anexemplary embodiment of the amplified communications signal 354. Thesecond amplifier module 806 includes an n-type metal oxide silicon(NMOS) transistor M₂ configured and arranged to operate as acommon-source amplifier based upon an external bias 860.

It should be noted that the common-source implementation of the firstamplifier module 802 and/or the second amplifier module 806 representsone exemplary configuration. Those skilled in the relevant art(s) mayimplement the first amplifier module 802 and/or the second amplifiermodule 806 differently in accordance with the teachings herein withoutdeparting from the scope and spirit of the present invention.

Operational Control Flow of the Communications Receiver

FIG. 10 is a flowchart 1000 of exemplary operational steps of thecommunications receiver used in the communications transceiver accordingto an exemplary embodiment of the present invention. The invention isnot limited to this operational description. Rather, it will be apparentto persons skilled in the relevant art(s) from the teachings herein thatother operational control flows are within the scope and spirit of thepresent invention. The following discussion describes the steps in FIG.10.

At step 1002, the operational control flow amplifies a receivedcommunication signal from a communication channel, such as thecommunications channel 104, using one or more antennas, one or morecopper cables, and/or one or more fiber optic cables. The receivedcommunication signal includes a desired communications signal and out ofband interference, the out of band interference occupying a spectrum offrequencies that is exclusive from a spectrum of frequencies occupied bythe desired communications signal. The operational control flowamplifies the received communication signal using a first amplifiermodule, such as the amplifier module 702 to provide an example, having again G₁. In an exemplary embodiment, step 1002 is optional. In thisexemplary embodiment, the operational control flow begins at step 1004.

At step 1004, the operational control flow removes out-of-bandinterference from an amplified communications signal of step 1004. Theoperational control flow may use a combination module, such as thecombination module 302 to provide an example, to subtract theout-of-band interference from the amplified communications signal ofstep 1004 to substantially reduce the out-of-band interference embeddedwithin the amplified communications signal of step 1004.

At step 1006, the operational control flow amplifies a noise reducedcommunications signal from step 1004. The operational control flowamplifies the received communication signal using a second amplifiermodule, such as the amplifier module 304 to provide an example, having again G₂.

At step 1008, the operational control flow downconverts an amplifiednoise reduced communications signal from step 1006 to approximately zeroHertz, referred to as DC or baseband, or to an intermediate frequency(IF) that is greater than DC based upon a first local oscillator signal,such as the first local oscillator signal 356 to provide an example. Theoperational control flow may use a first mixer, such as thedownconversion mixer 306 to provide an example, to downconvert theamplified noise reduced communications signal from step 1006.

At step 1010, the operational control flow replicates the out-of-bandinterference embedded within a recovered communication signal from step1008. The operational control flow may use a first filter, such as thefirst filter module 308 to provide an example, to filter out or removethe desired communications signal embedded within the recoveredcommunication signal from step 1008 leaving the out-of-bandinterference.

At step 1012, the operational control flow upconverts a replicatedout-of-band interference from step 1010 based upon a second localoscillator signal, such as the second local oscillator signal 362 toprovide an example. In an exemplary embodiment, a frequency of thesecond local oscillator signal is substantially similar to a frequencyof the first local oscillator signal. In another exemplary embodiment,the frequency of the second local oscillator signal is substantiallysimilar to a frequency of the first local oscillator signal but offsetin phase from each other. The operational control flow may use a secondmixer, such as the upconversion mixer 310 to provide an example, toupconvert replicated out-of-band interference from step 1010.

At step 1014, the operational control flow filters the recoveredcommunication signal from step 1008. The operational control flow mayuse a second filter, such as the second filter module 312 to provide anexample, to remove the out-of-band interference embedded within therecovered communication signal from step 1008 leaving only the desiredcommunications signal.

At step 1016, the operational control flow converts the desiredcommunication signal from step 1014 from an analog representation to adigital representation to provide the digital recovered informationsignal 350. The operational control flow may use an analog to digitalconverter, such as the ADC 314 to provide an example, to converts thedesired communication signal from step 1014 to the digitalrepresentation.

CONCLUSION

It is to be appreciated that the Detailed Description section, and notthe Abstract section, is intended to be used to interpret the claims.The Abstract section may set forth one or more, but not all exemplaryembodiments, of the present invention, and thus, are not intended tolimit the present invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries may be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

It will be apparent to those skilled in the relevant art(s) that variouschanges in form and detail can be made therein without departing fromthe spirit and scope of the invention. Thus, the present inventionshould not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. An apparatus, comprising: a first mixer configured to frequencytranslate a first communications signal to a first frequency using afirst local oscillator signal to provide a second communications signal;a filter module configured to filter the second communications signal toprovide a third communications signal; a second mixer configured tofrequency translate the third communications signal to a secondfrequency using a second local oscillator signal to provide a fourthcommunications signal, a frequency of the second local oscillator signalbeing substantially similar to a frequency of the first local oscillatorsignal, wherein the filter module is characterized by a first centerfrequency and a first frequency bandwidth corresponding to the firstfrequency, the second mixer being further configured to effectivelyfrequency translate the filter module to a second center frequencycorresponding to the second frequency while maintaining the firstfrequency bandwidth, the second center frequency being greater than thefirst center frequency.
 2. The apparatus of claim 1, wherein the firstfrequency includes at least one of a group consisting of: a basebandfrequency of approximately zero Hertz; and an intermediate frequency(IF), the IF being greater than the baseband frequency.
 3. The apparatusof claim 1, wherein the filter module is further characterized by afirst quality factor corresponding to the first frequency, the secondmixer effectively translating a characterization of the filter modulefrom the first quality factor to a second quality factor correspondingto the second frequency, the second quality factor being greater thanthe first quality factor.
 4. The apparatus of claim 3, wherein the firstquality factor represents a ratio of the first center frequency to thefirst frequency bandwidth and the second quality factor represents aratio of the second center frequency and the first frequency bandwidth.5. The apparatus of claim 1, wherein the filter module is implemented asa band pass filter.
 6. The apparatus of claim 1, further comprising: anamplifier module, coupled between the first mixer and the filter module,configured to amplify the second communications signal to provide afifth communications signal, wherein the filter module is configured tofilter the fifth communications signal to provide the thirdcommunications signal.
 7. The apparatus of claim 1, wherein the firstlocal oscillator signal and the second local oscillator signal areoffset in phase from each other.
 8. The apparatus of claim 7, whereinthe first local oscillator signal and the second local oscillator signalare offset in phase by approximately a group delay of the filter module.9. A method to effectively frequency translate a communications filter,the communications filter being characterized by a first centerfrequency and a first frequency bandwidth corresponding to a firstfrequency, from a first quality factor corresponding to the firstfrequency to a second quality factor corresponding to a secondfrequency, the second quality factor being greater than the firstquality factor, comprising: frequency translating a first communicationssignal to the first frequency using a first local oscillator signal toprovide a second communications signal; filtering the secondcommunications signal to provide a third communications signal;frequency translating the third communications signal to the secondfrequency using a second local oscillator signal, a frequency of thesecond local oscillator signal being substantially similar to afrequency of the first local oscillator signal, the frequencytranslating comprising: effectively frequency translating thecommunications filter to a second center frequency corresponding to thesecond frequency while maintaining the first frequency bandwidth thesecond center frequency being greater than the first center frequency.10. The method of claim 9, wherein the step of frequency translating thefirst communications signal comprises: frequency translating the firstcommunications signal to at least one of a group consisting of: abaseband frequency of approximately zero Hertz; and an intermediatefrequency (IF), the IF being greater than the baseband frequency. 11.The method of claim 9, wherein the communications filter is furthercharacterized by the first quality factor corresponding to the firstfrequency, and wherein the step of frequency translating the thirdcommunications signal comprises: effectively translating acharacterization of the communications filter from the first qualityfactor to the second quality factor.
 12. The method of claim 11, whereinthe first quality factor represents a ratio of the first centerfrequency to the first frequency bandwidth and the second quality factorrepresents a ratio of a second center frequency corresponding to thesecond frequency and the first frequency bandwidth.
 13. The method ofclaim 9, further comprising: amplifying the second communications signalto provide a fifth communications signal, and wherein the step offrequency translating the third communications signal comprises:frequency translating the fifth communications signal to the secondfrequency using the second local-oscillator signal.
 14. The method ofclaim 9, wherein the first local oscillator signal and the second localoscillator signal are offset in phase from each other.
 15. The method ofclaim 14, wherein the first local oscillator signal and the second localoscillator signal are offset in phase by approximately a group delay ofthe communications filter.
 16. The method of claim 9, wherein the stepof filtering the second communications signal comprises: using a bandpass filter to filter the second communications signal to provide thethird communications signal.
 17. A communications receiver, comprising:a combination module configured to combine a received communicationsignal and an upconverted replica noise signal to provide a noisereduced communications signal, the received communication signalincluding a desired communications signal and out of band interference;an amplifier module configured to amplify the noise reducedcommunications signal to provide an amplified communications signal; adownconversion mixer configured to frequency translate the amplifiedcommunications signal to a first frequency using a first localoscillator signal to provide a recovered communications signal; a filtermodule configured to filter the recovered communications signal toprovide a replica noise signal, the replica noise signal beingproportional to the out of band interference; and an upconversion mixerconfigured to frequency translate the replica noise signal to a secondfrequency using a second local oscillator signal to provide theupconverted replica noise signal, a frequency of the second localoscillator signal being substantially similar to a frequency of thefirst local oscillator signal, wherein the filter module ischaracterized by a first center frequency and a first frequencybandwidth corresponding to the first frequency, the upconversion mixerbeing configured to effectively frequency translate the filter module toa second center frequency corresponding to the second frequency whilemaintaining the first frequency bandwidth, the second center frequencybeing greater than the first center frequency.
 18. The communicationsreceiver of claim 17, further comprising: a second filter moduleconfigured to filter the recovered communications signal to provide arecovered information signal; and an analog to digital converter (ADC)configured to convert the recovered information signal from an analogrepresentation to a digital representation to provide a digitalrecovered information signal.
 19. The communications receiver of claim17, wherein the first frequency includes at least one of a groupconsisting of: a baseband frequency of approximately zero Hertz; and anintermediate frequency (IF), the IF being greater than the basebandfrequency.
 20. The communications receiver of claim 17, wherein thefilter module is further characterized by a first quality factorcorresponding to the first frequency, the upconversion mixer effectivelytranslating a characterization of the filter module from the firstquality factor to a second quality factor corresponding to the secondfrequency, the second quality factor being greater than the firstquality factor.
 21. The communications receiver of claim 20, wherein thefirst quality factor represents a ratio of the first center frequency tothe first frequency bandwidth and the second quality factor represents aratio of the second center frequency and the first frequency bandwidth.22. The communications receiver of claim 17, wherein the filter moduleis implemented as a band pass filter.
 23. The communications receiver ofclaim 17, wherein the first local oscillator signal and the second localoscillator signal are offset in phase from each other.
 24. Thecommunications receiver of claim 23, wherein the first local oscillatorsignal and the second local oscillator signal are offset in phase byapproximately a group delay of the filter module.
 25. The communicationsreceiver of claim 17, wherein the filter module is configured to removethe desired communications signal embedded within the recoveredcommunications signal, leaving the out of band interference embeddedwithin the recovered communications signal as the replica noise signal.26. An apparatus, comprising: a first mixer configured to frequencytranslate a first communications signal to a first frequency using afirst local oscillator signal to provide a second communications signal;a filter module configured to filter the second communications signal toprovide a third communications signal; and a second mixer configured tofrequency translate the third communications signal to a secondfrequency using a second local oscillator signal to provide a fourthcommunications signal; wherein the filter module is characterized by afirst quality factor corresponding to the first frequency, the secondmixer effectively translating a characterization of the filter modulefrom the first quality factor to a second quality factor correspondingto the second frequency, the second quality factor being greater thanthe first quality factor.
 27. The apparatus of claim 26, wherein thefirst quality factor represents a ratio of a first center frequencycorresponding to the first frequency to a first frequency bandwidth andthe second quality factor represents a ratio of a second centerfrequency corresponding to the second frequency and the first frequencybandwidth, the second center frequency being greater than the firstcenter frequency.
 28. The apparatus of claim 26, wherein the filtermodule is further characterized by a first center frequency and a firstfrequency bandwidth corresponding to the first frequency, the secondmixer being further configured to effectively frequency translate thefilter module to a second center frequency corresponding to the secondfrequency while maintaining the first frequency bandwidth, the secondcenter frequency being greater than the first center frequency.
 29. Theapparatus of claim 26, wherein the first frequency includes at least oneof a group consisting of: a baseband frequency of approximately zeroHertz; and an intermediate frequency (IF), the IF being greater than thebaseband frequency.
 30. The apparatus of claim 26, wherein the filtermodule is implemented as a band pass filter.
 31. The apparatus of claim26, further comprising: an amplifier module, coupled between the firstmixer and the filter module, configured to amplify the secondcommunications signal to provide a fifth communications signal, whereinthe filter module configured to filter the fifth communications signalto provide the third communications signal.
 32. The apparatus of claim26, wherein the first local oscillator signal and the second localoscillator signal are offset in phase from each other.
 33. The apparatusof claim 32, wherein the first local oscillator signal and the secondlocal oscillator signal are offset in phase by approximately a groupdelay of the filter module.